The use of individual VHF antennas arrayed in a linear or two-dimensional spatial configuration with relative phasing between them designed to achieve a particular radiation pattern dates back to the turn of the century. World War II provided the stimulus for the development of microwave radar, but all microwave radars utilized in the war featured only mechanical scanning of the radiation beams for tracking and surveillance. However, the art of electronic scanning advanced rapidly after the first demonstration of a ferrite scanned array by Huggins in 1958. The potential of highly agile electronic beam steering for handling multiple radar functions including multiple target tracking was detected immediately and intensive follow-on development was begun by a number of research institutions. As a result, a variety of phase shifter types and element feeds have been developed over the years. More recently, the development of optical methods of controlling the phase of microwave and millimeter wave signals have been accomplished.
One notable achievement among these is "[E]lectro-optical beamforming network for phased array antennas" taught by Richard A. Soref in U.S. Pat. No. 4,739,334 (Apr. 19, 1988) whose disclosure is hereby incorporated by reference into subject application, particularly the portion appearing in columns 4, 5, 6 and 7 and pertaining to Soref FIGS. 2 and 3. In the Soref patent, an optical signal emanating from a coherent laser source is divided into two paths, each path containing an electro-optic phase modulator. A microwave signal is applied to the modulator in the first path to provide an offset to the optical frequency by the amount of the microwave frequency. A given voltage (i.e. phase control signal) is applied to the modulator in the second path to phase-modulate (i.e. produce a specific amount of optical phase retardation) the optical signal traveling in that path. The optical signals from the two paths are, then, recombined on a photodetector which recovers the frequency difference between the two optical signals (i.e. the microwave frequency), now modulated by the phase that was imparted to the optical signal in the second path. In essence, the phase modulation imparted to the optical signal in the second path is transferred as phase modulation to the microwave signal. The mathematical expressions of these operations are presented in FIG. 2 of the Soref patent.